Projectors, even when projecting “black” still project some (e.g. grey, dark grey, whiteish, etc.) light onto the screen. When multiple projectors overlap onto a screen, the overlap regions become an even brighter “black” than the adjacent regions. The overlap regions hence distract from the projected content; for example, when content being projected is a mostly black scene (e.g. fireworks in a night sky), in the overlap regions, polygonal regions appear that are brighter than the surrounding darker area(s).
One solution is to move fixed geometry neutral density filter assemblies in and out of a light path frustum from a lens of a projector, to attempt to create a non-distracting optical blend for dark scenes, which can work for night simulators and other situations with dark scenes. However, such a solution does not tend to work well with projectors much higher than 8000 lumens without overheating and distorting the filters, unless they are quite large and far away from the lens, which can be awkward to arrange. While such filters can also be made with heat-tolerant materials, these materials can be harder to work with, can be expensive and/or can have inferior optical properties.